code: def test_tf_variable(self):
      x = tf.Variable(1.0, trainable=True)
      y = tensor_util.convert_nonref_to_tensor(x)
      self.assertIs(x, y)
      x = tf.Variable(1.0, trainable=False)
      y = tensor_util.convert_nonref_to_tensor(x)
      self.assertIs(x, y)
  
imports: import numpy
  import tensorflow.compat.v2
  from tensorflow_probability.python.bijectors import scale
  from tensorflow_probability.python.distributions import normal
  from tensorflow_probability.python.internal import tensor_util
  from tensorflow_probability.python.internal import test_util
  from tensorflow_probability.python.util import deferred_tensor
label_desc: Use image node_id 3 for calling the ConvertNonrefToTensorTest obj's underlying member method code with example usage: obj.test_tf_variable() without return types